1. Field of the Invention
This device relates to an adjustable top jaw and more particularly to an adjustable top jaw attached to a master jaw which is in turn attached to the chuck of a lathe or similar machine which top jaw is adjustable along a radial from the center of the chuck of such lath and which top jaw produces a clamping force along such radial.
2. Description of Related Art
Chucks, attached to lathes or similar devices, having a plurality of top jaws are currently available for holding work pieces in position on the chucks. FIG. 4A shows a typical prior art top jaw 1 located above a chuck 2. Typically, these prior art devices have a master jaw 1 recessed into a groove 5 located along radials extending outward from the center of the chuck 2. A one piece top jaw 1 is positionable above each master jaw 4 by moving the top jaw 1 to a desired position above the master jaw 4 and tightening a mounting screw 19 which extends through the top jaw 1 into a nut 6 restrained within a channel 7 in the master jaw 4. In this way, the top jaw 1 is held in the position it was set in above the master jaw 4 at the time the mounting screw 19 is tightened.
Typically, three such master and top jaw combinations exist on radials extending away from the center of the chuck. In this configuration, the master and top jaw combinations encircle an area approximately colineal with the axis of rotation of the chuck. However, once the prior art top jaws have been securely mounted above the master jaws, they are not capable of further movement along the radials extending from the center of the chuck. Therefore, they cannot provide a clamping force on a work piece located in the center of the convergence of the master and top jaw combinations. For this reason, a collet is placed in this convergence area between the top jaws to hold the work piece. When pressure is applied to the work piece at the end opposite the collet, the work piece is driven into the collet which because of its flared design wedges itself into the top jaws thereby putting clamping pressure on the work piece.
Although the use of collets allows the work piece to be clamped when pressure is applied to the work piece from the opposite end of the work piece, it is difficult for such collets to hold non-concentric work pieces. By non-concentric, it is meant that the part of the work piece held by the top jaws is not concentric with the part of the work piece to be acted on as the work piece is rotated by the chuck. In particular, once a non-concentric work piece is mounted in a collet, it is very difficult to adjust the top jaws to align the work piece section that will be worked with the axis of rotation of the chuck. This difficulty is largely the result of the lack of easy adjustment and particularly the lack of fine adjustment of the individual top jaws once the top jaws have been bolted to the master jaw. This is a problem in want of a solution.
Also, it is sometimes desirable to hold a work piece directly, instead of placing the work piece within a collet. The prior art devices do not allow for the work piece itself to be clamped by such top jaws without the use of collets. This is also a problem in want of a solution.